Passive optical networks (PONs) are a popular architecture for economically delivering telecommunications services to individual subscribers or groups of subscribers. Current PON deployments are typically based on IEEE 802.3ah (Ethernet PON (EPON)) or ITU-T G.984 (Gigabit-capable PON (GPON)). Both of these existing technologies have evolved into a next generation of networks, which is currently in early trial deployment. For example, IEEE has standardized 10GE-PON in 802.3av, while ITU-T has standardized XG-PON in the G.987 series of recommendations.
In both cases, the existing technologies have been extended in the next-generation standards to satisfy increased demand on service features and to take advantage of recent technological improvements. Developers of the next-generation standards propose replacement of existing infrastructure with next-generation equipment. As such, there has been no plan to retrofit next-generation features and benefits onto the current-generation products.
However, the current generation products are expected to have a long product life. To exploit the benefits available from some of the next-generation enhancements, it is valuable that existing devices (also referred to as “legacy devices”) be able to support at least some of the enhanced features of the next-generation equipment. Although this is desirable, it would be unacceptable to implement such feature support by completely re-defining upstream or downstream signals, because a legacy device would be unable to decode such signals.